The present invention relates to torque-generating steering devices, and more particularly, to such devices in which a relatively low-torque input is translated into a relatively high-torque steering output, with the aid of a source of pressurized fluid.
Torque generators of the type to which the present invention relates have been in commercial use for many years, and are illustrated and described in greater detail in U.S. Pat. No. Re. 25,291, assigned to the assignee of the present invention and incorporated herein by reference.
Torque generators include a valve means which is displaced from a neutral position to an operating (open) position by rotation of the steering wheel. When the valve means is open, pressurized fluid flows through the valve means and into a fluid pressure actuated displacement mechanism, such as a gerotor gear set, thereby generating a relatively high-torque steering output which is transmitted by means of an output shaft to a steering apparatus, such as the pinion gear of a rack and pinion device. Although the torque generator of the present invention may be used in various applications, it is especially advantageous (and used most commonly) in vehicle steering systems, and will be described in connection therewith.
The prior art torque generator has, as far as is known to applicant, always included valving of the open-center type, such that fluid would flow from the pump through the valving to the system reservoir whenever the torque generator is not being utilized, and the valving is in its neutral position. Although the operation of such open-center torque generators has been generally satisfactory, it has been necessary to provide a second pump in the event the vehicle includes any other hydraulic devices, beside the steering system. The provision of a second pump, and the associated plumbing and controls, on the types of vehicles which normally utilize torque generators becomes prohibitively expensive.